The present application relates to semiconductor manufacturing. More particularly, the present application relates to a method of removing a material portion of a base substrate utilizing a spalling process in which a reactive material stack is used to control the removal process.
Devices such as, for example, photovoltaic and electro-optical, that can be produced in thin-film form have three clear advantages over their bulk counterparts. First, by virtue of less material used, thin-film devices ameliorate the materials cost associated with device production. Second, low device weight is a definite advantage that motivates industrial-level effort for a wide range of thin-film applications. Third, if dimensions are small enough, devices can exhibit mechanical flexibility in their thin-film form. Furthermore, if a device layer is removed from a substrate that can be reused, additional fabrication cost reduction can be achieved.
Efforts to (i) create thin-film substrates from bulk materials (i.e., semiconductors) and (ii) form thin-film device layers by removing device layers from the underlying bulk substrates on which they were formed are ongoing. The recent development, see, for example, U.S. Patent Application Publication No. 2010/0311250 A1 to Bedell et al., of a novel layer transfer method referred to as ‘controlled spalling technology’ has permitted the fabrication of low-cost, thin-film, high quality substrates by removing a surface layer from a base substrate. The thin-film substrate layers that can be removed by this controlled spalling technology can be used to 1) increase the cost per Watt value of conventional photovoltaic technology or 2) permit fabrication of novel, high-efficiency photovoltaic, electronic and opto-electronic materials that are flexible and can be used to produce new products.
Control spalling of the type mentioned above relies on the intrinsic mechanical properties of a tensile stressor material for determining the fracture depth within the underlying bulk substrate. The use of such a process does not readily permit the ability to engineer the process in terms of fracture depth and/or residual stress. As such, there is a need to provide a material removal process which is capable of controlling fracture depth and/or residual stress as well as easing the requirements for the tensile stressor material in terms of level of stress and thickness.